The present invention relates to flat panel liquid crystal displays, and is directed more particularly to flat panel liquid crystal displays which utilize ultraviolet light to controllably illuminate an array of single or multi colored phosphor elements.
In attempting to produce displays which are less bulky than cathode ray tube type displays, a number of types of flat panel displays have been developed. One of these, known as a gas discharge type display, makes use of an array of phosphor elements which are individually addressed by an array of orthogonally disposed anode and cathode electrodes. One display of this type is described in U.S. Pat. No. 4,031,541, which issued in the name of Arisawa et al. on June 21, 1977.
Another type of flat panel display makes use of an array of colored strips which are aligned with the picture elements of a liquid crystal display. In displays of this type, the picture elements are addressed by controllably actuating the electrodes of the liquid crystal cells, thereby allowing light which is transmitted through or reflected from the cells to take on the color of the colored strips. One display of the latter type is described in U.S. Pat. No. 4,410,887, which issued in the name of Stolov et al. on Oct. 18, 1983.
Still another type of flat panel display makes use of a fluorescent plate which is located behind a liquid crystal display panel. In displays of this type, the switching of the liquid crystal cells makes selected parts of the fluorescent plate visible therethrough. One display of the latter type is described in U.S. Pat. No. 4,167,307, which issued in the name of Cirkler et al. on Sept. 11, 1979.
A still further type of flat panel display makes use of internally reflected visible light and a scattering type liquid crystal cell, but lacks a fluorescent viewing plate. One display of this type is described in copending application Ser. No. 605,508, filed Apr. 30, 1984, now U.S. Pat. No. 4,626,074 which application is owned by the assignee of the present invention.
Each of the above described types of displays has certain deficiencies which limit the usefulness thereof. Many displays of the above described types, for example, produce visible picture elements only during those times when the electrodes associated therewith are energized. Because all but very small displays will include hundreds of rows of such picture elements, the control circuitry of the display must include refresh circuitry for energizing each picture element at a relatively rapid rate, such as thirty times per second. Even with such refreshing, however, the fraction of the time that each picture element spends in its energized state is inversely proportional to the number of rows in the display. As a result, displays of the above described types often produce images which are relatively dim or have low contrast ratios.